Glossary
A-B
Last Updated July 24, 2000
compiled by Nick Sundt


A, B



A

Ablation - loss of a part (as ice from a glacier) by melting or vaporization.

Absolute Humidity - The ratio of the mass of water vapor to the volume occupied by a mixture of water vapor and dry air.(Source: US Department of Energy, 1999a).

Absorbent - A material that extracts one or more substances from a fluid (gas or liquid) medium on contact, and which changes physically and/or chemically in the process. The less volatile of the two working fluids in an absorption cooling device. (Source: US Department of Energy, 1999a).

Absorber - The component of a solar thermal collector that absorbs solar radiation and converts it to heat, or, as in a solar photovoltaic device, the material that readily absorbs photons to generate charge carriers (free electrons or holes). (Source: US Department of Energy, 1999a).

Absorption - The passing of a substance or force into the body of another substance. (Source: US Department of Energy, 1999a).

Absorption Chiller - A type of air cooling device that uses absorption cooling to cool interior spaces. (Source: US Department of Energy, 1999a).

Absorption Coefficient - In reference to a solar energy conversion devices, the degree to which a substance will absorb solar energy. In a solar photovoltaic device, the factor by which photons are absorbed as they travel a unit distance through a material. (Source: US Department of Energy, 1999a).

Absorption Cooling - A process in which cooling of an interior space is accomplished by the evaporation of a volatile fluid, which is then absorbed in a strong solution, then desorbed under pressure by a heat source, and then recondensed at a temperature high enough that the heat of condensation can be rejected to a exterior space. (Source: US Department of Energy, 1999a).

Absorption Refrigeration - A system in which a secondary fluid absorbs the refrigerant, releasing heat, then releases the refrigerant and reabsorbs the heat. Ammonia or water is used as the vapor in commercial absorption cycle systems, and water or lithium bromide is the absorber. (Source: US Department of Energy, 1999a).

Absorptivity - In a solar thermal system, the ratio of solar energy striking the absorber that is absorbed by the absorber to that of solar energy striking a black body (perfect absorber) at the same temperature. The absorptivity of a material is numerically equal to its emissivity.

acclimation (acclimatization) - Change that occurs in an organism to allow it to tolerate a new environment. (Source: Carbon Dioxide Information Analysis Center, 1990a).

ACH ( Air Changes per Hour) - Number of times in one hour that the air in your house is completely replaced with outside air. (Source: Lawrence Berkeley Laboratory, 1999)

Acid Rain - A term used to describe precipitation that has become acidic (low pH) due to the emission of sulfur oxides from fossil fuel burning power plants.(Source: US Department of Energy, 1999a).

Active Cooling - The use of mechanical heat pipes or pumps to transport heat by circulating heat transfer fluids. (Source: US Department of Energy, 1999a).

Active Power - The power (in Watts) used by a device to produce useful work. Also called input power.(Source: US Department of Energy, 1999a).

active solar energy - Solar radiation used by special equipment to provide space heating, hot water or electricity. (Source: California Energy Commission, 1999a)

active solar energy system - A system designed to convert solar radiation into usable energy for space, water heating, or other uses. It requires a mechanical device, usually a pump or fan, to collect the sun's energy. (Source: California Energy Commission, 1999a.)

Active Solar Heating Systems - A solar water or space-heating system that use pumps or fans to circulate the heat-transfer fluid from the solar collectors to a storage tank subsystem. (Source: US Department of Energy, 1999a).

Adiabatic - Without loss or gain of heat to a system. An adiabatic change is a change in volume and pressure of a parcel of gas without an exchange of heat between the parcel and its surroundings. In reference to a steam turbine, the adiabatic efficiency is the ratio of the work done per pound of steam, to the heat energy released and theoretically capable of transformation into mechanical work during the adiabatic expansion of a unit weight of steam. (Source: US Department of Energy, 1999a).

Adjustable Speed Drive - An electronic device that controls the rotational speed of motor-driven equipment such as fans, pumps, and compressors. Speed control is achieved by adjusting the frequency of the voltage applied to the motor. (Source: US Department of Energy, 1999a).

Adobe - A building material made from clay, straw, and water, formed into blocks, and dried; used traditionally in the southwestern U.S. (Source: US Department of Energy, 1999a).

Advection - the usually horizontal movement of a mass of fluid (as air or an ocean current); also : transport (as of pollutants or plankton) by such movement.

Aerobic Bacteria - Microorganisms that require free oxygen, or air, to live, and that which contribute to the decomposition of organic material in soil or composting systems. (Source: US Department of Energy, 1999a).

aerosol - Particulate material, other than water or ice, in the atmosphere ranging in size from approximately 10-3 to larger than 102 micrometers in radius. Aerosols are important in the atmosphere as nuclei for the condensation of water droplets and ice crystals, as participants in various chemical cycles, and as absorbers and scatterers of solar radiation, thereby influencing the radiation budget of the earth-atmosphere system, which in turn influences the climate on the surface of the Earth. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Aerosol - a product that relies on a pressurized gas to propel substances out of a container. Consumer aerosol products in the US have not used ozone-depleting substances (ODS) since the late 1970s because of voluntary switching followed by federal regulation. The Clean Air Act and EPA regulations further restricted the use of ODS for non-consumer products. All consumer products, and most other aerosol products, now use propellants that do not deplete the ozone layer, such as hydrocarbons and compressed gases. (Source: US Environmental Protection Agency, 1999b).

after­market - broad term that applies to any change after the original purchase, such as adding equipment not a part of the original purchase. As applied to alternative fuel vehicles, it refers to conversion devices or kits for conventional fuel vehicles. (Source: California Energy Commission, 1999a.)

AFUE (Annual Fuel Utilization Efficiency) - A measure of heating efficiency, in consistent units, determined by applying the federal test method for furnaces. This value is intended to represent the ratio of heat transferred to the conditioned space by the fuel energy supplied over one year. (Source: California Energy Commission, 1999a.)

Air - The mixture of gases that surrounds the earth and forms its atmosphere, composed of, by volume, 21 percent oxygen, 78 percent nitrogen. (Source: US Department of Energy, 1999a).

Air Change - A measure of the rate at which the air in an interior space is replace by outside (or conditioned) air by ventilation and infiltration; usually measured in cubic feet per time interval (hour), divided by the volume of air in the room. (Source: US Department of Energy, 1999a).

Air Collector - In solar heating systems, a type of solar collector in which air is heated in the collector. (Source: US Department of Energy, 1999a).

Air Conditioner - A device for conditioning air in an interior space. A Room Air Conditioner is a unit designed for installation in the wall or window of a room to deliver conditioned air without ducts. A Unitary Air Conditioner is composed of one or more assemblies that usually include an evaporator or cooling coil, a compressor and condenser combination, and possibly a heating apparatus. A Central Air Conditioner is designed to provide conditioned air from a central unit to a whole house with fans and ducts. (Source: US Department of Energy, 1999a).

Air Conditioning - The control of the quality, quantity, and temperature-humidity of the air in an interior space. (Source: US Department of Energy, 1999a).

Air Diffuser - An air distribution outlet, typically located in the ceiling, which mixes conditioned air with room air. (Source: US Department of Energy, 1999a).

air film - A layer of still air adjacent to a surface which provides some thermal resistance. (Source: California Energy Commission, 1999a.)

air film coefficient - A measure of the heat transfer through an air film. [See ASHRAE Table 1, ASHRAE Handbook, 1985 Fundamentals] (Source: California Energy Commission, 1999a.)

Air Infiltration Measurement - A building energy auditing technique used to determine and/or locate air leaks in a building shell or envelope. (Source: US Department of Energy, 1999a).

Air Register - The component of a combustion device that regulates the amount of air entering the combustion chamber. (Source: US Department of Energy, 1999a).

Air Retarder/Barrier - A material or structural element that inhibits air flow into and out of a building's envelope or shell. This is a continuous sheet composed of polyethylene, polypropylene, or extruded polystyrene. The sheet is wrapped around the outside of a house during construction to reduce air in-and exfiltration, yet allow water to easily diffuse through it. (Source: US Department of Energy, 1999a).

Air-Source Heat Pump - A type of heat pump that transfers heat from outdoor air to indoor air during the heating season, and works in reverse during the cooling season. (Source: US Department of Energy, 1999a).

Air Space - The area between the layers of glazing (panes) of a window.(Source: US Department of Energy, 1999a).

air-to-air heat exchanger - A device with separate air chambers that transfers heat between the conditioned air being exhausted and the outside air being supplied to a building. (Source: California Energy Commission, 1999a.)

Air-to-Air Heat Pump - see Air-Source Heat Pump. (Source: US Department of Energy, 1999a).

Air-to-Water Heat Pump - A type of heat pump that transfers heat in outdoor air to water for space or water heating. (Source: US Department of Energy, 1999a).

airborne particulates - Total suspended matter found in the atmosphere as solid pieces or liquid droplets. Airborne particulates include windblown dust, emissions from industrial processes, smoke from the burning of wood and coal, and the exhaust of motor vehicles. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Airlock Entry - A building architectural element (vestibule) with two airtight doors that reduces the amount of air infiltration and exfiltration when the exterior most door is opened. (Source: US Department of Energy, 1999a).

airmass - A widespread body of the atmosphere that gains certain meteorological or polluted characteristics while set in one location. The characteristics can change as it moves away. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Alcohol - A group of organic compounds composed of carbon, hydrogen, and oxygen; a series of molecules composed of a hydrocarbon plus a hydroxyl group; includes methanol, ethanol, isopropyl alcohol and others. (Source: US Department of Energy, 1999a).

Albedo - The ratio of light reflected by a surface to the light falling on it. (Source: US Department of Energy, 1999a).

Algae - Primitive plants, usually aquatic, capable of synthesizing their own food by photosynthesis. (Source: US Department of Energy, 1999a).

algal blooms - Sudden spurts of algal growth due to greatly increased amounts of phosphorus entering the aquatic ecosystem from sewage systems and agricultural fertilizers. Excessive growth of the algae causes destruction of many of the higher links of the food web. Algae that die and sink to the bottom at the end of the growing season stimulate massive growth of bacteria the following year, resulting in depletion of oxygen in the deeper water layers. This may result in fish kills and replacement with less valuable species who may be more tolerant of increased phosphorus levels. Deoxygenation also may cause chemical changes in the mud on the bottom, producing increased quantities of chemicals and toxic gases. All these changes further accelerate the eutrophication (aging) of the aquatic ecosystem. (Source: Carbon Dioxide Information Analysis Center, 1990a).

alkalinity - A pressure- and temperature-independent property of seawater that determines in part the carbon content of seawater. Carbonate alkalinity is the sum of the concen- tration of bicarbonate plus two times the concentration of the carbonate ions. Total alkalinity is the amount of acid required to bring seawater to a pH at which all dissolved inorganic carbon becomes freely exchangeable. The alkalinity of the oceans is determined with potentiometric or normal titration techniques that detect and measure the presence of bicarbonate, carbonate, and borate ions. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Alternating Current - A type of electrical current, the direction of which is reversed at regular intervals or cycles; in the U.S. the standard is 120 reversals or 60 cycles per second; typically abbreviated as AC. (Source: US Department of Energy, 1999a).

alternative energy sources - See RENEWABLE ENERGY. (Source: California Energy Commission, 1999a.)

Alternative Fuels - A popular term for "non-conventional" transportation fuels derived from natural gas (propane, compressed natural gas, methanol, etc.) or biomass materials (ethanol, methanol). (Source: US Department of Energy, 1999a).

alternative fuel vehicle (AFV) - motor vehicles that run on fuels other than petroleum-based fuels. As defined by the National Energy Policy Act (EPAct), this excludes reformulated gasoline as an alternative fuel. (Source: California Energy Commission, 1999a.)

alternative (transportation) fuels - as defined by the National Energy Policy Act (EPAct) the fuels are: methanol, denatured ethanol and other alcohols, separately or in mixtures of 85 percent by volume or more (or other percentage not less than 70 percent as determined by U.S. Department of Energy rule) with gasoline or other fuels; CNG; LNG; LPG; hydrogen; "coal-derived liquid fuels;" fuels "other than alcohols" derived from "biological materials;" electricity, or any other fuel determined to be "substantially not petroleum" and yielding "substantial energy security benefits and substantial environmental benefits." (Source: California Energy Commission, 1999a.)

Alternator - A generator producing alternating current by the rotation of its rotor, and which is powered by a primary mover. (Source: US Department of Energy, 1999a).

Ambient Air - The air external to a building or device. (Source: US Department of Energy, 1999a).

Ambient Temperature - The temperature of a medium, such as gas or liquid, which comes into contact with or surrounds an apparatus or building element. (Source: US Department of Energy, 1999a).

Ammonia - A colorless, pungent, gas (NH3) that is extremely soluble in water, may be used as a refrigerant; a fixed nitrogen form suitable as fertilizer. (Source: US Department of Energy, 1999a).

Amorphous Semiconductor - A non-crystalline semiconductor material that has no long-range order. (Source: US Department of Energy, 1999a).

Ampere - A unit of measure for an electrical current; the amount of current that flows in a circuit at an electromotive force of one Volt and at a resistance of one Ohm. Abbreviated as amp. (Source: US Department of Energy, 1999a).

Amp-Hours - A measure of the flow of current (in amperes) over one hour. (Source: US Department of Energy, 1999a).

anadromous fish - Fish that spend their adult lives in the sea but swim upriver to freshwater spawning grounds to reproduce. Salmon are an example of anadromous fish. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Anaerobes - Organisms that live and are active only in the absence of oxygen. (Source: US Energy Information Administration, 1999a).

Anaerobic Bacteria - Microorganisms that live in oxygen deprived environments. (Source: US Department of Energy, 1999a).

Anaerobic decomposition - The breakdown of molecules into simpler molecules or atoms by microorganisms that can survive in the partial or complete absence of oxygen. (Source: US Energy Information Administration, 1999a).

Anaerobic Digestion - The complex process by which organic matter is decomposed by anaerobic bacteria. The decomposition process produces a gaseous byproduct often called "biogas" primarily composed of methane, carbon dioxide, and hydrogen sulfide. (Source: US Department of Energy, 1999a).

Anaerobic Digester - A device for optimizing the anaerobic digestion of biomass and/or animal manure, and possibly to recover biogas for energy production. Digester types include batch, complete mix, continuous flow (horizontal or plug-flow, multiple-tank, and vertical tank), and covered lagoon. (Source: US Department of Energy, 1999a).

Anaerobic Lagoon - A holding pond for livestock manure that is designed to anaerobically stabilize manure, and may be designed to capture biogas, with the use of an impermeable, floating cover. (Source: US Department of Energy, 1999a).

analog (climate) - A large-scale weather pattern of the past that is similar to a current situation in its essential characteristics. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Anhydrous Ethanol - One hundred percent alcohol; neat ethanol. (Source: US Department of Energy, 1999a).

Anemometer - An instrument for measuring the force or velocity of wind; a wind gauge. (Source: US Department of Energy, 1999a).

Angle of Incidence - In reference to solar energy systems, the angle at which direct sunlight strikes a surface; the angle between the direction of the sun and the perpendicular to the surface. Sunlight with an incident angle of 90 degrees tends to be absorbed, while lower angles tend to be reflected. (Source: US Department of Energy, 1999a).

Angle of Inclination - In reference to solar energy systems, the angle that a solar collector is positioned above horizontal. (Source: US Department of Energy, 1999a).

animal waste conversion - Process of obtaining energy from animal wastes. This is a type of biomass energy. (Source: California Energy Commission, 1999a.)

Annex I Parties (UN Framework Convention on Climate Change) - The industrialized countries are listed in this annex to the Climate Convention. They include the 24 original OECD members, the European Union, and 14 countries with economies in transition (Croatia, Liechtenstein, Monaco and Slovenia joined at COP-3, and the Czech Republic and Slovakia replaced Czechoslovakia). The parties were to return their greenhouse gas emissions to 1990 levels by the year 2000 and also accept emission targets for the period 2008-12. (Source: UN Climate Change Secretariat, 1999a)

Annex II Parties (UN Framework Convention on Climate Change) - The rich countries listed in this annex to the Climate Convention have a special obligation to help developing countries with financial and technological resources. They include the 24 original OECD members plus the European Union. (Source: UN Climate Change Secretariat, 1999a)

Alliance of Small Island States (AOSIS) - The AOSIS is an ad-hoc coalition of low-lying and island countries. These countries are particularly vulnerable to sea-level rise and share common positions on climate change. The 42 members and observers are American Samoa, Antigua and Barbuda, Bahamas, Barbados, Belize, Cape Verde, Comoros, Cook Islands, Cuba, Cyprus, Dominica, Federated States of Micronesia, Fiji, Grenada, Guam, Guinea-Bissau, Guyana, Jamaica, Kiribati, Maldives, Malta, Marshall Islands, Mauritius, Nauru, Netherlands Antilles, Niue, Palau, Papua New Guinea, Samoa, Sao Tome and Principe, Seychelles, Singapore, Solomon Islands, St. Kitts & Nevis, St. Lucia, St. Vincent and the Grenadines, Suriname, Tonga, Trinidad and Tobago, Tuvalu, US Virgin Islands, and Vanuatu. (Source: UN Climate Change Secretariat, 1999a)

Annual Fuel Utilization Efficiency (AFUE) - The measure of seasonal or annual efficiency of a residential heating furnace or boiler. It takes into account the cyclic on/off operation and associated energy losses of the heating unit as it responds to changes in the load, which in turn is affected by changes in weather and occupant controls. (Source: US Department of Energy, 1999a).

Annual Load Fraction - That fraction of annual energy demand supplied by a solar system. (Source: US Department of Energy, 1999a).

annual maximum demand - The greatest of all demands of the electrical load which occurred during a prescribed interval in a calendar year. (Source: California Energy Commission, 1999a.)

Annual Solar Savings - The annual solar savings of a solar building is the energy savings attributable to a solar feature relative to the energy requirements of a non-solar building. (Source: US Department of Energy, 1999a).

Anode - The positive pole or electrode of an electrolytic cell, vacuum tube, etc. (see also sacrificial anode). (Source: US Department of Energy, 1999a).

ANSI - American National Standards Institute is the national organization that coordinates development and maintenance of consensus standards and sets rules for fairness in their development. ANSI also represents the USA in developing international standards. (Source: California Energy Commission, 1999a.)

Antarctic Ice Sheet - See ice sheet.

Antarctic "ozone hole" - Refers to the seasonal depletion of stratospheric ozone in a large area over Antarctica. See ozone layer.(Source: US Environmental Protection Agency, 1999a).

Anthracite (coal) - A hard, dense type of coal, that is hard to break, clean to handle, difficult to ignite, and that burns with an intense flame and with the virtual absence of smoke because it contains a high percentage of fixed carbon and a low percentage of volatile matter. (Source: US Department of Energy, 1999a).

anthropogenic - Man made. Usually used in the context of emissions that are produced as the result of human activities. (Source: Carbon Dioxide Information Analysis Center, 1990a).

anticyclone (high-pressure area) - An atmospheric high-pressure closed circulation with clockwise rotation in the Northern Hemisphere, counterclockwise in the Southern Hemisphere, and undefined at the Equator. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Antifreeze Solution - A fluid, such as methanol or ethylene glycol, added to vehicle engine coolant, or used in solar heating system heat transfer fluids, to protect the systems from freezing. (Source: US Department of Energy, 1999a).

Antireflection Coating - A thin coating of a material applied to a photovoltaic cell surface that reduces the light reflection and increases light transmission. (Source: US Department of Energy, 1999a).

Aperture - An opening; in solar collectors, the area through which solar radiation is admitted and directed to the absorber. (Source: US Department of Energy, 1999a).

Apparent Day - A solar day; an interval between successive transits of the sun's center across an observer's meridian; the time thus measured is not equal to clock time. (Source: US Department of Energy, 1999a).

Apparent Power (kVA) - This is the voltage-ampere requirement of a device designed to convert electric energy to a non-electrical form.(Source: US Department of Energy, 1999a).

Appliance - A device for converting one form of energy or fuel into useful energy or work. (Source: US Department of Energy, 1999a).

Appliance Energy Efficiency Ratings - The ratings under which specified appliances convert energy sources into useful energy, as determined by procedures established by the U.S. Department of Energy. (Source: US Department of Energy, 1999a).

appliance saturation - A percentage telling what proportion of all households in a given geographical area have a certain appliance. (Source: California Energy Commission, 1999a.)

Arctic haze - A persistent winter diffuse layer in the Arctic atmosphere whose origin may be related to long-range transport of midlatitude continental anthropogenic pollutants. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Argon - A colorless, odorless inert gas sometimes used in the spaces between the panes in energy efficient windows. This gas is used because it will transfer less heat than air. Therefore, it provides additional protection against conduction and convection of heat over conventional double-pane windows.(Source: US Department of Energy, 1999a).

Array (Solar) - Any number of solar photovoltaic modules or solar thermal collectors or reflectors connected together to provide electrical or thermal energy. (Source: US Department of Energy, 1999a).

Ash - The non-combustible residue of a combusted substance composed primarily of alkali and metal oxides. (Source: US Department of Energy, 1999a).

ASHRAE - Abbreviation for the American Society of Heating, Refrigeration, and Air-Conditioning Engineers. (Source: US Department of Energy, 1999a).

ASTM - Abbreviation for the American Society for Testing and Materials, which is responsible for the issue of many standard methods used in the energy industry. (Source: US Department of Energy, 1999a).

Asynchronous Generator - A type of electric generator that produces alternating current that matches an existing power source. (Source: US Department of Energy, 1999a).

atmosphere (An) - A standard unit of pressure representing the pressure exerted by a 29.92-in. column of mercury at sea level at 45 degrees latitude and equal to 1000 g/cm2. (Source: Carbon Dioxide Information Analysis Center, 1990a).

atmosphere (The) - The mixture of gases surrounding the Earth. The Earth’s atmosphere consists of about 79.1 percent nitrogen (by volume), 20.9 percent oxygen, 0.036 percent carbon diox-ide and trace amounts of other gases. The atmosphere can be divided into a number of layers according to its mixing or chemical characteristics, generally determined by its thermal properties (temperature). The layer nearest the Earth is the troposphere, which reaches up to an altitude of about 8 kilometers (about 5 miles) in the polar regions and up to 17 kilometers (nearly 11 miles) above the equator. The stratosphere, which reaches to an altitude of about 50 kilometers (31miles) lies atop the troposphere. The mesosphere, which extends from 80 to 90 kilo-meters atop the stratosphere, and finally, the thermosphere, or ionosphere, gradually diminishes and forms a fuzzy border with outer space. There is relatively little mixing of gases between layers. (Source: US Environmental Protection Agency, 1999a)

Atmospheric Pressure - The pressure of the air at sea level; one standard atmosphere at zero degrees centigrade is equal to 14.695 pounds per square inch (1.033 kilograms per square centimeter). (Source: US Department of Energy, 1999a).

Atrium - An interior court to which rooms open. (Source: US Department of Energy, 1999a).

Attic - The usually unfinished space above a ceiling and below a roof. (Source: US Department of Energy, 1999a).

Attic Fan - A fan mounted on an attic wall used to exhaust warm attic air to the outside. (Source: US Department of Energy, 1999a).

Attic Vent - A passive or mechanical device used to ventilate an attic space, primarily to reduce heat buildup and moisture condensation. (Source: US Department of Energy, 1999a).

Audit (Energy) - The process of determining energy consumption, by various techniques, of a building or facility. (Source: US Department of Energy, 1999a).

Automatic Damper - A device that cuts off the flow of hot or cold air to or from a room as controlled by a thermostat. (Source: US Department of Energy, 1999a).

Automatic (or Remote) Meter Reading System - A system that records the consumption of electricity, gas, water, etc, and sends the data to a central data accumulation device. (Source: US Department of Energy, 1999a).

Automobile size classifications - Size classifications of automobiles are established by the Environmental Protection Agency (EPA) as follows: (Source: Center for Transportation Analysis, 1999a)

Minicompact - less than 85 cubic feet of passenger and luggage volume.
Subcompact - between 85 to 100 cubic feet of passenger and luggage volume.
Compact - between 100 to 110 cubic feet of passenger and luggage volume.
Midsize - between 110 to 120 cubic feet of passenger and luggage volume.
Large - more than 120 cubic feet of passenger and luggage volume.
Two seater - automobiles designed primarily to seat only two adults.
Station wagons are included with the size class for the sedan of the same name.

Auxiliary Energy or System - Energy required to operate mechanical components of an energy system, or a source of energy or energy supply system to back-up another. (Source: US Department of Energy, 1999a).

Availability - Describes the reliability of power plants. It refers to the number of hours that a power plant is available to produce power divided by the total hours in a set time period, usually a year. (Source: US Department of Energy, 1999a).

Availability Factor - A percentage representing the number of hours a generating unit is available to produce power (regardless of the amount of power) in a given period, compared to the number of hours in the period. (Source: US Energy Information Administration, 1997a.)

Available Heat - The amount of heat energy that may be converted into useful energy from a fuel. (Source: US Department of Energy, 1999a).

Average Cost - The total cost of production divided by the total quantity produced. (Source: US Department of Energy, 1999a).

Average Demand - The demand on, or the power output of, an electrical system or any of its parts over an interval of time, as determined by the total number of kilowatt-hours divided by the units of time in the interval. (Source: US Department of Energy, 1999a).

Average Wind Speed (or Velocity) - The mean wind speed over a specified period of time. (Source: US Department of Energy, 1999a).

Avoided Cost - The incremental cost to an electric power producer to generate or purchase a unit of electricity or capacity or both. (Source: US Department of Energy, 1999a).

Axial Fans - Fans in which the direction of the flow of the air from inlet to outlet remains unchanged; includes propeller, tubaxial, and vaneaxial type fans. (Source: US Department of Energy, 1999a).

Axial Flow Compressor - A type of air compressor in which air is compressed in a series of stages as it flows axialy through a decreasing tubular area. (Source: US Department of Energy, 1999a).

Axial Flow Turbine - A turbine in which the flow of a steam or gas is essentially parallel to the rotor axis. (Source: US Department of Energy, 1999a).

Azimuth (Solar) - The angle between true south and the point on the horizon directly below the sun. (Source: US Department of Energy, 1999a).

AWG - The abbreviation for American Wire Gauge; the standard for gauging the size of wires (electrical conductors). (Source: US Department of Energy, 1999a).

Awning - An architectural element for shading windows and wall surfaces placed on the exterior of a building; can be fixed or movable. (Source: US Department of Energy, 1999a).


B

Backdrafting - The flow of air down a flue/chimney and into a house caused by low indoor air pressure that can occur when using several fans or fireplaces and/or if the house is very tight. (Source: US Department of Energy, 1999a).

Backup Energy System - A reserve appliance; for example, a standby generator for a home or commercial building. (Source: US Department of Energy, 1999a).

Bacteria - Single-celled organisms, free-living or parasitic, that break down the wastes and bodies of dead organisms, making their components available for reuse by other organisms. (Source: US Department of Energy, 1999a).

Baffle - A device, such as a steel plate, used to check, retard, or divert a flow of a material. (Source: US Department of Energy, 1999a).

Bagasse - The fibrous material remaining after the extraction of juice from sugarcane; often burned by sugar mills as a source of energy. (Source: US Department of Energy, 1999a).

Baghouse - An air pollution control device used to filter particulates from waste combustion gases; a chamber containing a bag filter. (Source: US Department of Energy, 1999a).

Balance of System - In a solar energy system, refers to all components other than the collector. In terms of costs, it includes design costs, land, site preparation, system installation, support structures, power conditioning, operation and maintenance costs, indirect storage, and related costs. (Source: US Department of Energy, 1999a).

Balance Point - An outdoor temperature, usually 20 to 45 degrees Fahrenheit, at which a heat pump's output equals the heating demand. Below the balance point, supplementary heat is needed. (Source: US Department of Energy, 1999a).

Baling - A means of reducing the volume of a material by compaction into a bale. (Source: US Department of Energy, 1999a).

Ballast - A device used to control the voltage in a fluorescent lamp. (Source: US Department of Energy, 1999a).

Ballast Efficacy Factor - The measure of the efficiency of fluorescent lamp ballasts. It is the relative light output divided by the power input. (Source: US Department of Energy, 1999a).

Ballast Factor - The ratio of light output of a fluorescent lamp operated on a ballast to the light output of a lamp operated on a standard or reference ballast. (Source: US Department of Energy, 1999a).

Barrel (petroleum) - 42 U.S. gallons (306 pounds of oil or 5.78 million Btu). One barrel of oil has an energy content of 6 million British thermal units. It takes one barrel of oil to make enough gasoline to drive an average car from Los Angeles to San Francisco and back (at 18 miles per gallon over the 700-mile round trip). (Source: US Department of Energy, 1999a and California Energy Commission, 1999a).

Basal Metabolism - The amount of heat given off by a person at rest in a comfortable environment; approximately 50 Btu per hour (Btu/h). (Source: US Department of Energy, 1999a).

Baseboard Radiator - A type of radiant heating system where the radiator is located along an exterior wall where the wall meets the floor. (Source: US Department of Energy, 1999a).

baseline forecast - A prediction of future energy needs which does not take into account the likely effects of new conservation programs that have not yet been started. (Source: California Energy Commission, 1999a.)

Baseload Capacity - The power output of a power plant that can be continuously produced. (Source: US Department of Energy, 1999a).

Baseload Demand - The minimum demand experienced by a power plant. (Source: US Department of Energy, 1999a).

Baseload Power Plant - A power plant that is normally operated to generate a base load, and that usually operates at a constant load; examples include coal fired and nuclear fueled power plants. (Source: US Department of Energy, 1999a).

Basement - The conditioned or unconditioned space below the main living area or primary floor of a building. (Source: US Department of Energy, 1999a).

Base Power - Power generated by a utility unit that operates at a very high capacity factor. (Source: US Department of Energy, 1999a).

base rate - That portion of the total electric or gas rate covering the general costs of doing business unrelated to fuel expenses. (Source: California Energy Commission, 1999a.)

Batt/Blanket - A flexible roll or strip of insulating material in widths suited to standard spacings of building structural members (studs and joists). They are made from glass or rock wool fibers. Blankets are continuous rolls. Batts are pre-cut to four or eight foot lengths. (Source: US Department of Energy, 1999a).

Battery - An energy storage device composed of one or more electrolyte cells. (Source: US Department of Energy, 1999a).

Battery Energy Storage - Energy storage using electrochemical batteries. The three main applications for battery energy storage systems include spinning reserve at generating stations, load leveling at substations, and peak shaving on the customer side of the meter. (Source: US Department of Energy, 1999a).

Bbl - The abbreviation for barrel. (Source: US Energy Information Administration, 1999b)

Bcf - The abbreviation for 1 billion cubic feet. (Source: US Energy Information Administration, 1999b)

Beadwall ™ - A form of movable insulation that uses tiny polystyrene beads blown into the space between two window panes. (Source: US Department of Energy, 1999a).

Beam Radiation - Solar radiation that is not scattered by dust or water droplets. (Source: US Department of Energy 1999a).

Bearing Wall - A wall that carries ceiling rafters or roof trusses. (Source: US Department of Energy, 1999a).

Benefits Charge - The addition of a per unit tax on sales of electricity, with the revenue generated used for or to encourage investments in energy efficiency measures and/or renewable energy projects. (Source: US Department of Energy, 1999a).

benthic organism (benthos) - A form of aquatic plant or animal life that is found on or near the bottom of a stream, lake, or ocean. (Source: Carbon Dioxide Information Analysis Center, 1990a).

benthic region - The bottom layer of a body of water. (Source: Carbon Dioxide Information Analysis Center, 1990a).

benzene - A type of colorless liquid hydrocarbon that can be used as a motor fuel. Its chemical symbol is C6H6. (Source: California Energy Commission, 1999a.)

bi-fuel vehicle - A vehicle with two separate fuel systems designed to run on either fuel, using only one fuel at a time. These systems are advantageous for drivers who do not always have access to an alternative fuel refueling station. Bi-fuel systems are usually used in light-duty vehicles. One of the two fuels is typically an alternative fuel. (Source: California Energy Commission, 1999a.)

Bimetal - Two metals of different coefficients of expansion welded together so that the piece will bend in one direction when heated, and in the other when cooled, and can be used to open or close electrical circuits, as in thermostats. (Source: US Department of Energy, 1999a).

Binary Cycle - Combination of two power plant turbine cycles utilizing two different working fluids for power production. The waste heat from the first turbine cycle provides the heat energy for the operation of the second turbine, thus providing higher overall system efficiencies. (Source: US Department of Energy, 1999a).

Binary Cycle Geothermal Plants - Binary cycle systems can be used with liquids at temperatures less than 350 F (177 C). In these systems, the hot geothermal liquid vaporizes a secondary working fluid, which then drives a turbine. (Source: US Department of Energy, 1999a).

Biochemical Oxygen Demand - The weight of oxygen taken up mainly as a result of the oxidation of the constituents of a sample of water by biological action; expressed as the number of parts per million of oxygen taken up by the sample from water originally saturated with air, usually over a period of five days at 20 degrees centigrade. A standard means of estimating the degree of contamination of water. (Source: US Department of Energy, 1999a).

Bioconversion - The conversion of one form of energy into another by the action of plants or microorganisms. The conversion of biomass to ethanol, methanol, or methane. (Source: US Department of Energy, 1999a).

biodiesel - A biodegradable transportation fuel for use in diesel engines that is produced through the transesterfication of organically- derived oils or fats. It may be used either as a replacement for or as a component of diesel fuel. (Source: California Energy Commission, 1999a.)

Bioenergy - The conversion of the complex carbohydrates in organic material into energy. (Source: US Department of Energy, 1999a).

Biofuels - Organic materials, such as wood, waste, and alcohol fuels, burned for energy purposes. (Source: US Energy Information Administration, 1999a).

Biogas - A combustible gas created by anaerobic decomposition of organic material, composed primarily of methane, carbon dioxide, and hydrogen sulfide. (Source: US Department of Energy, 1999a).

Biogasification or biomethanization - The process of decomposing biomass with anaerobic bacteria to produce biogas. (Source: US Department of Energy, 1999a).

Biogenic - Produced by the actions of living organisms. (Source: US Energy Information Administration, 1999a).

biogeochemical cycle - The chemical interactions among the atmosphere, biosphere, hydrosphere, and lithosphere. (Source: Carbon Dioxide Information Analysis Center, 1990a).

biological productivity - The amount of organic matter, carbon, or energy content that is accumulated during a given time period. (Source: Carbon Dioxide Information Analysis Center, 1990a).

biomass - The total dry organic matter or stored energy content of living organisms that is present at a specific time in a defined unit (community, ecosystem, crop, etc.) of the Earth's surface. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Biomass Energy - Energy produced by combusting biomass materials such as wood. The carbon dioxide emitted from burning bio-mass will not increase total atmospheric carbon dioxide if this consumption is done on a sustainable basis (i.e., if in a given period of time, regrowth of biomass takes up as much carbon dioxide as is released from biomass com-bustion). Biomass energy is often suggested as a replace-ment for fossil fuel combustion.(Source: US Environmental Protection Agency, 1999a)

Biomass Fuel - Biomass converted directly to energy or converted to liquid or gaseous fuels such as ethanol, methanol, methane, and hydrogen. (Source: US Department of Energy, 1999a).

Biomass Gasification - The conversion of biomass into a gas, by biogasification (see above) or thermal gasification, in which hydrogen is produced from high-temperature gasifying and low-temperature pyrolysis of biomass. (Source: US Department of Energy, 1999a).

Biophotolysis - The action of light on a biological system that results in the dissociation of a substrate, usually water, to produce hydrogen. (Source: US Department of Energy, 1999a).

biosphere - The portion of Earth and its atmosphere that can support life. The part (reservoir) of the global carbon cycle that includes living organisms (plants and animals) and life-derived organic matter (litter, detritus). The terrestrial biosphere includes the living biota (plants and animals) and the litter and soil organic matter on land, and the marine biosphere includes the biota and detritus in the oceans. (Source: Carbon Dioxide Information Analysis Center, 1990a).

biota - The animal and plant (fauna and flora) life of a given area. (Source: Carbon Dioxide Information Analysis Center, 1990a).

Bituminous Coal - A dense coal, usually black, sometimes dark brown, often with well-defined bands of bright and dull material, used primarily as fuel in steam-electric power generation, with substantial quantities also used for heat and power applications in manufacturing and making coke. Bituminous coal is the most abundant coal in active U. S. mining regions. Its moisture content usually is less than 20 percent. The heat content of bituminous coal ranges from 21 to 30 million Btu per short ton on a moist, mineral-matter-free basis. The heat content of bituminous coal consumed in the United States averages 24 million Btu per short ton, on the as-received basis (i.e., containing both inherent moisture and mineral matter). (Source: US Energy Information Administration, 2000a.)

Blackbody - An ideal substance that absorbs all radiation falling on it, and reflecting nothing. (Source: US Department of Energy, 1999a).

blackout - A power loss affecting many electricity consumers over a large geographical area for a significant period of time. (Source: California Energy Commission, 1999a.)

Blower - The device in an air conditioner that distributes the filtered air from the return duct over the cooling coil/heat exchanger. This circulated air is cooled/heated and then sent through the supply duct, past dampers, and through supply diffusers to the living/working space. (Source: US Department of Energy, 1999a).

Blower Door - A device used by energy auditors to pressurize a building to locate places of air leakage and energy loss. (Source: US Department of Energy, 1999a).

Blown In Insulation (see also Loose Fill) - An insulation product composed of loose fibers or fiber pellets that are blown into building cavities or attics using special pneumatic equipment. (Source: US Department of Energy, 1999a).

Boiler - A vessel or tank where heat produced from the combustion of fuels such as natural gas, fuel oil, or coal is used to generate hot water or steam for applications ranging from building space heating to electric power production or industrial process heat. (Source: US Department of Energy, 1999a).

Boiler Feedwater - The water that is forced into a boiler to take the place of that which is evaporated in the generation of steam. (Source: US Department of Energy, 1999a).

Boiler Horsepower - A unit of rate of water evaporation equal to the evaporation per hour of 34.5 pounds of water at a temperature of 212 degrees Fahrenheit into steam at 212 degrees F. (Source: US Department of Energy, 1999a).

Boiler Pressure - The pressure of the steam or water in a boiler as measured; usually expressed in pounds per square inch gauge (psig). (Source: US Department of Energy, 1999a).

Boiler Rating - The heating capacity of a steam boiler; expressed in Btu per hour (Btu/h), or horsepower, or pounds of steam per hour. (Source: US Department of Energy, 1999a).

Bone (Oven) Dry - In reference to solid biomass fuels, such as wood, having zero moisture content. (Source: US Department of Energy, 1999a).

Bone Dry Unit - A quantity of (solid) biomass fuel equal to 2,400 pounds bone dry. (Source: US Department of Energy, 1999a).

Booster Pump - A pump for circulating the heat transfer fluid in a hydronic heating system. (Source: US Department of Energy, 1999a).

Bottled Gas. A generic term for liquefied and pressurized gas, ordinarily butane, propane, or a mixture of the two, contained in a cylinder for domestic use. (Source: US Department of Energy, 1999a).

Brine - Water saturated or strongly impregnated with salt. (Source: US Department of Energy, 1999a).

British Thermal Unit (Btu) - The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories. For example, it takes about 2,000 Btus to make a pot of coffee. (Source: US Department of Energy, 1999a and California Energy Commission, 1999a.).

brownout - A controlled power reduction in which the utility decreases the voltage on the power lines, so customers receive weaker electric current. Brownouts can be used if total power demand exceeds the maximum available supply. The typical household does not notice the difference. (Source: California Energy Commission, 1999a.)

Building Energy Ratio - The space-conditioning load of a building. (Source: US Department of Energy, 1999a).

Building Envelope - The structural elements (walls, roof, floor, foundation) of a building that encloses conditioned space; the building shell. (Source: US Department of Energy, 1999a).

Building Heat-Loss Factor - A measure of the heating requirements of a building expressed in Btu per degree-day. (Source: US Department of Energy, 1999a).

Building Orientation - The relationship of a building to true south, as specified by the direction of its longest axis. (Source: US Department of Energy, 1999a).

Bulb - The transparent or opaque sphere in an electric light that the electric light transmits through. (Source: US Department of Energy, 1999a).

Bulk Density - The weight of a material per unit of volume compared to the weight of the same volume of water. (Source: US Department of Energy, 1999a).

bulk power supply - Often this term is used interchangeably with wholesale power supply. In broader terms, it refers to the aggregate of electric generating plants, transmission lines, and related-equipment. The term may refer to those facilities within one electric utility, or within a group of utilities in which the transmission lines are interconnected. (Source: California Energy Commission, 1999a.)

Burner Capacity - The maximum heat output (in Btu per hour) released by a burner with a stable flame and satisfactory combustion. (Source: US Department of Energy, 1999a).

Bus (electrical) - An electrical conductor that serves as a common connection for two or more electrical circuits; may be in the form of rigid bars or stranded conductors or cables. (Source: US Department of Energy, 1999a).

busbar - The power conduit of an electric power plant; the starting point of the electric transmission system. (Source: US Department of Energy, 1999a).

Busbar Cost - The cost of producing electricity up to the point of the power plant busbar. (Source: US Department of Energy, 1999a).

butane - A hydrocarbon gas found in the earth along with natural gas and oil. Butane turns into a liquid when put under pressure. It is sold as bottled gas. It is used to run heaters, stoves and motors, and to help make petrochemicals. (Source: California Energy Commission, 1999a.)

buy through - An agreement between utility and customer to import power when the customer's service would otherwise be interrupted.

Bypass - An alternative path. In a heating duct or pipe, an alternative path for the flow of the heat transfer fluid from one point to another, as determined by the opening or closing of control valves both in the primary line and the bypass line. (Source: US Department of Energy, 1999a).